Abseiling is a technique used to descend steep surfaces such as cliff faces and is often used by persons involved in activities such as mountain climbing, canyoning and caving. In order to abseil down a cliff face, one end of a rope is made fast at the top of the cliff and the person making the descent then slides down the rope. The rope is passed either around the body of the person or more usually through a descender attached to a harness worn by the person such that the passage of the rope around the body or through the descender provides sufficient friction to slow the rate of descent to a safe speed.
A descender comprises rope engaging surfaces around and between which the rope travels, along a tortuous path, to provide frictional engagement between the rope and the descender. The rate of descent is normally controlled by holding the free or tail end of the rope to control the tension on the rope where it emerges from the descender and thereby to control the degree of frictional engagement between the rope and the descender which in turn controls the rate of descent.
Descenders used in abseiling vary greatly in performance and complexity, there being a variety of relatively simple devices which rely on frictional engagement between the rope and metal rings or racks about which the rope is wrapped, and a number of more complex descenders which incorporate a braking mechanism which allows the friction between the rope and the descender to be varied other than by simply controlling the free or tail end of the rope. The earliest of these more complex devices had a handle or lever which when operated tended to increase the friction between the descender and the rope. This type of descender was not a great improvement over the more simple devices as the brake was not self-engaging and therefore, if the user was knocked unconscious, he would fall in the same way as the user of the earlier devices.
The present invention is derived from a class of descenders wherein the variable braking action of the descender increases when the handle is released. Usually, the force required to initiate the braking action is provided by the frictional engagement of the descender with the rope travelling therethrough. It is also possible to have arrangements which are operated by springs. Spring operated arrangements have the disadvantage that the restoring force of the spring may reduce with age or the spring may become damaged without this being noticed by the user, thereby decreasing the effectiveness of the descender.
An improved type of descender was disclosed in U.S. Pat. No. 4,596,314 to the present applicant which provides a descender having a simplicity of construction and operation which was not achieved by earlier prior art descenders. U.S. Pat. No. 4,596,134 describes a descender for use in abseiling which includes a base having a connection means for connection to a harness and a pivotal member pivotally mounted on the base about a pivot axis extending generally normal to the base, the pivot axis being spaced from the connection means. The pivotal member has first and second spaced projections for engaging a rope, the projections both extend generally parallel to the pivot axis with the first projection being disposed about the pivot axis and the second projection being located on the opposite side of the pivot axis with respect to the connection means: The pivotal member defines a handle means to selectively pivot the pivotal member relative to the base. The base further includes a stop located adjacent the second projection which limits movement of the pivotal member.
In use, a rope passing around and between the first and second projections and between the second projection and the stop surface had a resistance force applied thereto which was a maximum when the handle means was released and the tension of the rope causes the second projection to bear against the stop and press the rope between the stop and the second projection. The disclosure of this United States patent is incorporated herein by reference.
A disadvantage of the descender disclosed in U.S. Pat. No. 4,596,314 is that the actuation and release of the self-engaging brake can in some situations be rather abrupt or jerky. For example, it can be difficult for inexperienced users to smoothly control the braking action. Also the descender exhibits a tendency to fall very quickly when the brake is released.
An improved type of descender was disclosed in U.S. Pat. No. 5,597,052. That descender provided a modification to the descender shown in U.S. Pat. No. 4,596,314 which allowed the user to smoothly control the braking action and thereby avoid or minimise the jerkiness.
The improvement relied on replacing the stop surface by a variable braking mechanism having braking surface defined by a cam pivotally mounted on the base, controlled by a handle/lever. While this descender is an improvement over the descender shown in U.S. Pat. No. 4,596,314, substantial additional manufacturing costs are associated with the provision of the cam surface and associated lever. Also the provision of two handles on the descender can make the device more complicated to understand and use, particularly for the inexperienced users, for whom the device is intended.